1982 300 SD A/C pressures

[oilslick]

I just wanted to see if there were any specifics as far as pressures. I have searched but for some reason I can't seem to find what I am looking for. I have checked the pressures with the correct gauges and the following is what I found.

Ambient Temp.....................................80-85 F
Vent Temp .....................................55-60 F
System Refrigerant..............................R-134a
High Side @ 1500 rpms.........................200-225 PSI
Low Side @ 1500 rpms.............................25-40 PSI

It seems that he compressor cuts out for too long while going down the freeway. The system cools much better at idle but as soon as you accelerate above 2,000 rpms the compressor cuts out and the vent temp begins to rise. On a really hot day the car can be rather hard to keep cool. As long as the compressor is running it stays bearable.

Just thought I would ask before I took it to the A/C shop. Thanks!

Kevin

To begin with, THANK YOU VERY MUCH FOR SUCH A CONCISE POST!!!!!!!!!! Unfortunately very few A/C question posts give temps and pressures and precise symptoms.

Unfortunately I am not intimately familiar with the 126 climate control system, but I would be surprised if it is much different in function and fundamentals than most of the others.

The puzzling part is the compressor dropping out. Is the clutch gap possibly a little too wide? I'm not sure what the max is on your car, but I would check it and find out what the max air gap is allowed. I also might spray down the clutch with brake cleaner while it is cool.

The controls should not be cutting out the compressor, but it's possible that the 126 cars are a pressure cycling system. As I said, I'm not familiar with that chassis. If it is a pressure cycling system it might be worth making note of the pressures at which the compressor drops out at 2,000 RPM.

Hope this helps,

[leathermang]

Is your AUX fan coming on ?
A faulty pressure switch might cause this symptom.
I wonder if the pressure switch was made for 134a pressures ?
Did you install a 134a TXvalve when the system was converted to 134a ?

[oilslick]

It was already converted before I purchased the car. However, I did replace the AUX Fan but not the switch. The fan locked up and burned the fuse...bad fan bearing. The new fan comes on and cuts off pretty normal. I will replace the old switch though.

There is also a milky look to the sight glass, possibly millions of bubbles? These bubbles go away occasionally especially when you initially rev the engine but above 2,000 rpms the compressor cuts out.

I will be going to the A/C shop tomorrow morning, wish me luck!

Kevin

P.S. Thanks LarryBible and Leathermang for replying to my post. You guys are the best, from what I've read in the archives, when it comes to A/C diagnostics and repairs. Thanks so very much!

[leathermang]

Ok,, hope the shop helps you out...
but if you get a chance... with the ambient temperature over 70 degrees... if you stabilize the system for at least 10 minutes... then slowly increase the engine rpm's to the point that the compressor cuts out... while looking at the sight glass... use a watch and time how long it takes those bubbles to stop flowing after the compressor cuts out...
Let us know the results if you get to try this... 45 seconds is the usual threshold time... more or less than that tends to indicate refrigerant charge..
but if your refrigerant actually looks milky that is almost certainly water in the sytem....

[oilslick]

I will let you guys know what happens.

Kevin

[oilslick]

I now have a better A/C system. It's cooling more consistent now. I had the system evacuated and pulled a vacuum for about 30 to 45 minutes at 28 hg. The bubbles are ALMOST non-existent in the sight glass now and I am able to get a good 48-55 degrees out of the center vents. For some reason the outer vents blow colder; maybe a degree or two, maybe three.

Anyway, the compressor kicks out around 48-45 degress and does not re-engage until the vent temps reach the 58-61 degree point. That has been as long as 60 seconds and as short as 20. Oh yes, the ambient temp is in the 80 to 83 range with moderate humidity.

I have 25-30 psi on the low side and 200-225 psi on the high side at idle and a slight drop on the low side when increasing rpms. THe drop is about 2 or 3 psi. The high side has a slight increase of about the same.

Okay, tell me what is wrong with my numbers or what to search for about the compressor cycling the way it is.

Kevin